The present invention relates to a silicone caulking composition prepared from a silicone emulsion reinforced with a nonsiliceous filler such as calcium carbonate. The silicone caulking compositions contain certain silyl ureas as adhesion promoters.
In copending application Ser. No. 200,482, filed May 31, 1988, and assigned to the same assignee as the present invention, certain curable silicone latex compositions are described made by the emulsification of a silanol-terminated polydiorganosiloxane with a nonionic surfactant. The pH of the silicone emulsion is adjusted with carboxylic acid to a pH between 4 and 6 which can then be optionally combined with an acidic colloidal silica along with a crosslinker and a tin condensation catalyst in the form of a stannoxane. The silicone emulsion is further combined with a nonsiliceous filler, such as calcium carbonate, to form a silicone caulk. Although the aforementioned caulking compositions have been found to exhibit significantly improved shelf stability, particularly in the absence of acidic colloidal silica, they do not adhere well to a variety of substrates.
In U.S. Pat. No. 4,506,058, Ashby et al., there is described self-bonding room temperature vulcanizable compositions (RTV) which utilizes certain bis(polyalkoxysilyl) ureas as adhesion promoters. The bissilyl ureas of Ashby et al. are incorporated into the base (RTV) mixture of ingredients under moisture-free substantially nonacidic conditions.
The present invention is based on the discovery that incorporation of an effective amount of certain bissilyl ureas, as defined hereinafter, to a reinforced base formulation of an aqueous emulsion of a nonionically stabilized silanol-terminated polydiorganosiloxane at a pH of about 4-6 containing a silane cross-linker and tin catalyst can provide a shelf stable silicone caulk capable of forming an elastomer upon removal of water, exhibiting excellent adhesion to a variety of substrates, such as steel or aluminum. Suprisingly, the bissilyl urea adhesion promoter is not adversely affected under acidic aqueous condition over an extended shelf period.